Compact 1500-Ton Press

The Bearings
Caterpillar’s Danville, KY plant makes bushings and pins that allow parts to pivot in machines such as large wheel loaders, and it also assembles prototype machines. CAT’s volume has nearly doubled over the past three years, and it has been on the lookout for ways to improve manufacturing execution. A sophisticated new press is one of those ways.

Production Equipment Upgrade
Personnel at CAT’s 187,000 sq ft Danville plant, say that a new press used to assemble proprietary bushing/pin/seal assemblies has greatly increased the plant’s capabilities. (See the sidebar, “What the Press is Used For.”) They refer to the press as a “bump press” because its work is accomplished with a relatively modest amount of hydraulic cylinder travel. The new press is much more compact than the methods and equipment previously used. Plant personnel point out that an old 500-ton press had a separate hydraulic room. Also, some of the pressing work formerly had to be taken to other locations (such as CAT’s Sumter, SC facility) because of equipment capacity limitations at Danville.
Additionally, the component itself has evolved into a more precise and sophisticated device. Old-style pin assemblies utilized cone bearings with auto-lube systems. This approach has several drawbacks. Tolerances are relatively loose, autolube systems are prone to leakage, and field replacement is labor-intensive.

The new “cartridge” approach to the design of pivot pin assemblies addresses all three of the drawbacks associated with the old approach. The cartridges feature sealed-in lubricant, tighter tolerances, and easy replacement while maintaining the tight tolerances.

Installation
Installation of the press was simple and straightforward. After the four corner feet were bolted using leveling shims as needed, three utility connections were made:

• 120 V, single-phase control power;

• 460 V, three-phase power (approximately 3 hp);

• Shop air supply.

Operation
Eight different-length pins are presently assembled using the press. Those other than the longest pin are accommodated by means of special riser blocks.
 The compact size of the 1500 ton press can be seen in the photo of the entire unit. The hydraulic cylinder, visible at the top, has a 2-in. stroke.This press does far more than apply hydraulic force. Its mechanical design and digital control system work together to both simplify the process for the operator and provide a high level of safety. Let’s take a pictorial tour of highlights of a typical operating sequence.

Operation of the shuttle table is immediately halted if the control station E-stop button is pressed or if the machine vision system detects an obstruction in the cylinder path. In either case, the shuttle table must be returned to its fullyextended position before the cycle can be re-initiated.

When an assembly has moved into place within the press and the guard doors have closed, the operator can zero the laser measuring system to the magnetic target. Following that, the operator selects cylinder pressure and time duration of pressing and retracting via the control station’s touch pad display. For safety, pressure selection is limited to a specific range. As with the shuttle table cycle, the operator must press two buttons simultaneously in order to initiate press cylinder operation.

Upon completion of the press cycle, the laser readout displays the completed dimension in green if it is within a preselected acceptable range, or in red if it is outside the acceptable range. (An unacceptable dimension may require “rebumping.”)

Uncluttered, yet presenting lots of information, the operator interface indicates all of the parameters shown above, upper left; as well as the position of the guard doors and shuttle table.

The operator must press two buttons simultaneously to initiate the operation. As the shuttle table moves the assembly into the press, machine vision (the green device next to the cylinder, figure 6) checks the cylinder’s path to verify that it is free of obstructions.

Maintenance
Normal maintenance is of an entirely routine nature, such as periodic hydraulic oil and filter changes, cooling fan clean-off, checking bolt torques, and checking air pressure and regulator, filter, water separator, lubricator, and the like.Annual recalibration of electronic controls is recommended in order to maintain accuracy of pressing force settings.

The Bottom Line
Even though it takes big numbers to characterize this press, such as a 2000-ton cylinder, 12-in. thick tool steel platens,and 5-in. diameter tie rods joining the platens, the unit is compact, requiring only about 25 sq ft of floor space and a small control station. And this compact package affords convenience, accuracy, and a high level of safety, so it delivers what CAT needs in the drive to improve manufacturing execution.

What the Press is Used For
Whether the assembly work involves production models or prototype units, the job of the Enerpac press is to prepare pivot-pin assemblies, referred to as cartridges. Figure 8 shows a prototype unit undergoing evaluation.

Shawn Gallagher is a Territory Manager for Enerpac